1. Field of the Invention
This invention relates generally to sheets embossed with diffraction grating and/or hologram patterns. More particularly, the invention concerns a fibrous sheet or fabric whereon the diffraction grating and/or hologram pattern is embossed directly on a surface of the fibrous sheet or fabric without detrimentally affecting the flexibility and breathability of the sheet or fabric.
2. Description of the Prior Art
Rainbow and hologram images have been produced by diffracting light from patterns of very fine grooves on the surface of various plastic sheets or films. Such patterns are mass-produced by embossing the plastic surface under heat and pressure with a metal die (or "stamper") having in its face the desired pattern in relief Known methods for producing hologram images on fabrics generally are rather complicated and detrimentally affect certain properties of the fabrics. For example, U.S. Pat. No. 4,956,040 discloses a method in which a precut foil having a hologram pattern embossed on its surface is laminated between a clear polyester coating and an adhesive scrim backing to form a laminate which is then adhered to a woven fabric. International Patent Application WO 91/12365 discloses forming a laminate of an outer metal foil bearing a holographic image, a middle layer of plastic size and a lower layer of fabric. These two disclosures are typical of the many methods involving production of a hologram pattern on a plastic film or metal foil layer which is laminated to the surface of a fabric. Although such processes can provide strong holographic images, the portions of the fabric that are covered with the film or foil lose the breathability, flexibility and surface tactile aesthetics of the original fabric without the film or foil. International Patent Application WO 89/01063 and Japanese Patent Publication SHO 63-309639 disclose embossing a hologram pattern on a thin plastic film, slitting the film into long ribbons of 1 to 20 mm width, forming the ribbons into yarns and then making a fabric of the ribbons. However, fabrics made with such yarns are limited to localized glitter color effects and cannot produce large scale rainbow or hologram images. Further, the dimensions of the slit-ribbon yarns are usually too large for the ribbons to be used in apparel fabrics. For apparel fabrics, fiber diameter typically is in the range of 0.001 to 0.1 mm.
In other methods aimed at providing hologram images on fabrics, series of fine grooves are formed on individual filaments which are then formed into fabrics. For example, Japanese Patent SHO 62-170510 discloses simultaneously co-spinning two molten polymers into a filament and then dissolving one of the two polymer components to form fine grooves on the filament surface parallel to the axis of the filament. U.S. Pat. No. 4,842,405 discloses another method in which the fine grooves are cut in the surfaces of filaments with laser beams. Because the distances between adjacent filaments in the yarn and fabric are not controlled to be at multiples of groove width and because these filaments typically are made into yarns by plying, interlacing, crimping and/or twisting, the groove patterns are disrupted and fabrics made from such filament yarns do not provide full rainbow or hologram images but provide only glitter points or line segments of glitter randomly distributed on the fabric surface.
In summary, with regard to diffraction or hologram images on fabrics, the art discloses how to produce either (a) large rainbow and hologram images on impermeable plastic films or metal foils which are laminated or stitched to the surface of the fabric, but with accompanying detrimental effects on the breathability and tactile aesthetics of the fabric or (b) fine, microscopic glitter points on fabrics made from filaments having fine longitudinal grooves without affecting other fabric characteristics. Accordingly, an aim of the present invention is to provide a fibrous sheet or fabric having large rainbow and/or hologram images without incorporating an impermeable plastic or metal foil that would detrimentally affect the flexibility and breathability of the sheet or fabric.